Stabilized photographic silver halide emulsions



United States atent O STABILIZED PHQTOGRAPHIC SILVER HALIDE MULSIONS L ha N Drawing. Application March 8, 1957" Serial No. 644,733 T 11 Claims.(Cl. 96-109) This invention relates to fog-inhibiting agents andstabilizers for photographic emulsions, and to photographic emulsionscontaining them.

It is well known that photographic emulsions on storage tend to losesensitivity and to become spontaneously developablewithout exposure tolight. There is'normally a detectable amountof the silver saltreducedduringdevelopment in the areas where no exposure was given{ thisis commonly called fog, and sometimes called chemical fog where it isnecessary to distinguish betwc'en it and the eifects of accidentalexposure to radiation; in this invention, we are not concerned with thelatter;

Fog depends both on the emulsion and the conditions of. development; fora given emulsion it increases With the degree of development; Withconstant development conditions, it tends to increase with time,temperature and relative humidity of storage conditions; it is commonpractice to make accelerated tests of the stability of photo graphicemulsions by storage at increased temperature or humidity, or both. Itis, of course, desirable to have emulsions as stable as possible underthe conditions of high temperature and humidity which may occur intropical climates, for example. Fog usually appears over the 1 wholearea of the sensitive coating, {but when'severe, it frequently isnon-uniform; Fog may also be caused by exposure to chemicals, forexample, hydrogen sulfide, and other reactive sulfur compounds, hydrogenperoxide vapor, and strongly reducing materials; While antifoggants andstabilizers may protect, to some extent, agains t such effects, it isnormally understood that an antifoggant protects again st spontaneousgrowth of fog during prolonged storage or storage at hightemperaturesand li lmtdities, or during development to maximum contrastand speed,

or both. v

It is, accordingly, anobject of our invention to provide a method forstabilizing photographic silver halide emulsions. Another object is tomaintain the sensitivity and fog of photographic silver halide emulsionsat or close to initial optimum 'valuesunder keeping conditions of hightemperature and humidity. A further-object is toprovide photographicsilver halide emulsions containing antifoggarits -or stabilizers. Otherobjects will become apparent from a consideration of the followiugdescription and examples.

According'to our invention photographic silver halide 1 to obtainincreased sensitivity.

2,8?,0l5 Patented Jan. 20, 195% (e. g., methyl, ethyl, n-propyl,n-butyl, isobutyl, n-hexyl, n-octyl, n-dodecyl, n-cetyl, etc.,especially a lower alkyl group containing from 1 to 4 carbon atoms) or aheteroy y oup. su h s b nzat i zyl. n aazyl. pyridyl, etc, and Drepresents the non metallic atoms necessary to complete a monocyclicaromaticgroup of the benzene series, such as benzene or substitutedbenzenes (i. e., benzene substituted by such radicals as chlorine,bromine, methoxyl, ethoxyl, methyl, ethyl, tc.).

lt'has also been found in certain instances that a number of thecompounds embraced by Formula I above serve to increase the sensitivityof: photographic silver halide emulsions, inaddition to stabilizing theemulsions or providing an antifoggant effect. However, the foginhibitingeffect is more general than the sensitizing eficct, and for this reason,these compounds are referred to below as antifoggants or fog-inhibitors.

The fog-inhibitors which we propose to use are added to the emulsion durn he. pre ets-of. naautas to avoid loss of sensitivity and to inhibitthe growth of fog with passage of time under non-ideal conditions ofstorage.

A solution of the compounds of the invention when added in suitableconcentration, before coating, to unsensitized, chemically sensitized,or. optically sensitized photographic emulsions may not appreciablyaffect the sensitometric values for sensitivity and fo when measurementsare made soon after coating. When sensitometric measurements are made atappreciable intervals of time, at elevatedtemperatures and dry orsomewhat humid conditions, these compounds do stabilize photographic-speed and maintainfog at alow-level. I

Thepreparatiori of silverhalide emulsions involves three separateoperations: '(1) the emulsificationand digestion :or ripening of thesilver halide, (2) the freeing of the emulsion from excess solublesalts, usually by washing, and (3) the second digestion ofafter-ripening prior to digestion.

. th sis R er ata- Mas s an ass I Listed below are a number ofcompounds-coming within the scope of Formula I above which we have foundto be particularly advantageous in practicingour inven-2,8-dihydro-3-oigobenzoisothiazole (av s t -GHI c ll :2,3 si siro-z thaos snz is th aaqls Q SC I ll 2,3-dihydro-2-ethy1-3: oxcheuaoisothiaaoleI (MeesflThe Theory of 2-n-butyl-2,3-dihydro-3-oxobenzoisothlaz01e2-cety1-2,3dihydro-3-oxobenzolsothtazole /N--C\ G H O2-benzothiazy1-2,3-dihydro-3-oxoheuzoisothiazole (7) s N C uHzs (n)2,3-dlhydro-2-n-dodecy1-3-oxohenzoisothiazole varying halide content canadvantageously be used. The

antifoggant compounds used in our invention have been found particularlyuseful when employed in conjunction with gelatinosilver-bromiodideemulsions, although they can also be advantageously employed forstabilizing other silver halide emulsions, such asgelatino-silverchloride, bromide, chlorobromide, chlorobromiodide, etc.

The emulsions can also be chemically sensitized by any of the acceptedprocedures. The emulsions can be digested with naturally active gelatin,or sulfur compounds can be added such as those described in Sheppard U.S. Patent 1,574,944 and ,U.' S. 1,623,499, and Sheppard and Brigham U.S. Patent 2,410,689.

The emulsions can also be treated with salts of the noble metals such asruthenium, rhodium, palladium, iridium and platinum, all of which belongto group VIII of the periodic table of elements and have an atomicweight greater than 100. Representative compounds are ammoniumchloropalladate, potassium chloroplatinate and sodium chloropalladite,which are used for sensitizing in amounts below that which produces anysubstantial fog inhibition, as described in Smith and Trivelli U. S.Patent 2,448,060, and as antifoggants in higher amounts, as described inTrivelli andSmith US. Patents 2,566,245 and 2,566,263.

The emulsions can also bechemically sensitized with gold salts asdescribedin'Waller and Dodd U. S. Patent 2,399,083, or stabilized withgold salts as described in Damschroder U. S. Patent 2,597,85 6 and Yutzyand Leermakers U. S. Patent 2,597,915, Suitable compounds are potassiumchloroaurite, potassium aurithiocyanate, potassium chloroauratqaurictrichloride and Z-aurosulfobenzothiazole methochlorid'e.

The emulsions can also be chemically sensitized with reducing agentssuch as stannous salts (Carroll U. S. Patent 2,487,850), polyamines suchas diethylene triamine (Lowe and Jones U. S. Patent 2,518,698),polyamines, such as spermine (Lowe and Allen U. S. Patent 2,521,925), orbis-(fi-aminoethynsulfide and its watersoluble salts (Lowe and Jones U.S. Patent 2,521,926).

The emulsions can also be stabilized with the mercury compounds ofAllen, Byers and Murray U. S. Patent 2,728,663, Carroll and Murray U. S.Patent 2,728,664, and Leubner and Murray U. S. Patent 2,728,665.

The stabilizing combinations of our compounds are effective in thepresence or absence of optical sensitizing dyes. Since opticalsensitizing may affect stability of emulsions with respect tosensitivity, fog and latent image changes, the action of the compoundsof this invention is not completely independent of optical sensitizingor other emulsion variables. We have found, however, that bothunsensitized emulsions and emulsions sensitized with cyanine ormerocyanine dyes, or both, can be treated according to our invention.

The antifoggant and/or stabilizing action was determined by incubationof the emulsions for one week at a temperature of F. and constantrelative humidity (obtained by placing the emulsions'in closedcontainers, the ambient temperature being about 70 F. and relativehumidity about 50-55 percent prior to sealing the containers).

The etficiency of the various antifoggants was determined by measuringthe speed, gamma and fog of the incubated emulsions containing anantifoggant and comparing these measurements with those of the samebatch of emulsion before incubation. Also, similar measurements weremade with a photographic emulsion containing no antifoggant both beforeand after incubation.

The tests were made using high speed, negative-type silver bromiodideemulsions (coated on cellulose acetate supports), which had beenpanchromatically sensitized with a cyanine dye and chemically sensitizedwith sulfur and gold compounds. The test films were exposed on anintensity scale sensitometer and developed for 5 minutes in a developerhaving the following composition:

Water to make l'liter.

The speed, gamma and fog for each of the emulsion coatlngs were thenmeasured as indicated above. The re sults obtained are given in thefollowlng table.

, Fresh Coatings Ineubatad Coatings Compound Example (gJmol.

AgX) 30/E' Gam- Fog 30/E Garn- Fog Speed ma Speed ma In a manner similarto that illustrated in the above examples, other compounds selected fromthose represented by the above general Formula I can be incorporated inphotographic emulsions for the purpose of stabilization. Thefog-inhibiting agents useful in practicing our invention can be used invarious kinds of photographic emulsions. In addition to being useful inordinary non-sensitized emulsions, they can also be used in ortho- Achromatic, panchromatic and X-ray emulsions. If used with sensitizingdyes, they can be added to the emulsion before or after the dyes areadded. Suitable dispersing agents for the silver halide emulsionsstabilized according to our invention comprise gelatin, or othercolloids, such as collodion, albumen, celluloseorg'anic derivatives,synthetic resins, etc.

The optimum amount of fog-inhibiting agent can be determined by making;the customary tests employed in emulsion making. f course, the optimumamount for a given emulsion will varydepending on the presence ofemulsion iaddenda, such as chemical ;sensitizers, optical sensitizers,etc. In general, we have found that from 0.001 to 5.0 g. offog-inhibting agent per mole of silver halide is suflicient for thepurposes of our invention.

Instead of adding the fog-inhibiting agent directly to the photographicemulsion, it is sometimes desirable to incorporate the fog-inhibitingagent in a separate layer which is placed in contact with the silverhalide emulsion layer which is to be stabilized. Under such conditions,of

.course,--.it .is advisable to use a higher. concentration offog-inhibiting agent than indicated above.

I I v The antifoggants ;of our invention functionadvantageou'sly in acidfor alkaline photographic silver halideernul'sions. 7

It has also been noted that certainnitrogen-containing compounds otherthan those of Formula I above can be used in photographic gsilver halideemulsions, frequently to give antifoggant .or stabilizing effects. Suchcompounds include, for example, "ethylfurfurylidenedicarba'mate, TheFurans," A. -C. :S. "Monograph No. 119' (1953), page 374, which can alsobe named furfurylidenebisurethane (ethyl ester). Other relatednitrogencontaining compounds, such as ethylidenebisurethane,

benzylidenebisurethane, thienylidenebisurethane, etc., can 35,

Example A.2-cetyl-2,3-dihydr0-3-0x0benz0is0thiazole Two solutions wereprepared as follows:

Solution A. grams of n-cetylamine were dissolved in 50 cc. of pyridineand 200 cc. of anhydrous carbon tetrachloride with warming.

Solution B.7 grams of dithiodibenzoylchloride were i "added to 100 cc.of carbon tetrachloride and chlorinewas passed into the mixture untilthe dithiodibenzoylchloride had dissolved. Nitrogen was then passed intothe container holding the solution to remove excess chlorine. Thesolution was then filtered.

Solution A was warmed to 55 C. to keep in solution and Solution B wasslowly added to Solution A with stirring. The temperature rose to 60 C.and crystals appearing to be pyridine hydrochloride separated. Aftercooling to ambient temperature, the reaction mixture was poured onto oneliter of ice and made acid (with hydrochloric acid) to Congo red. Thecarbon tetrachloride layer was separated and washed with cold water. Thecarbon tetrachloride solution was dried over calcium chloride,decolorized with decolorizing carbon and dried over magnesium sulfate.The solution was filtered and concentrated under reduced pressure on thesteam bath. The concentrated solution was dissolved in ethyl alcohol,treated once again with decolorizing carbon, filtered and The put in therefrigerator. The desired material crystallized Two solutions wereprepared as follows:

Solution A.-7 grams of dithiodibenzoylchloride were added to cc. ofcarbon tetrachloride and chlorine passed into the mixture until completesolution ensued. Excess chlorine was then removed by passing in nitrogengas and the solution was filtered.

Solution B.6 grams of Z-aminobenzothiazole were dissolved in a mixtureof 50 cc. of pyridine and cc. of carbon tetrachloride.

Solution A was-added to Solution B slowly, the temperature rising to 45C. during the addition. The desired product separated immediately ascrystalline material. The reaction mixture was allowed to stand for anadditional 1.5 hours and then filtered. The filter cake was washed with100 cc. of water to remove any pyridine hydrochloride present.Thedesired product was recrystallized from dimethyl- 'forin'amid'e,collected on a filter, leached in diethyl ether,

Analysis.Calcd. for C, 59.2%; H, 2.8%; N, 9.9%.

Found: C, 59.4%;1-1, 2.4%; N, 9.9%.

What we claim as our invention and desire secured by Letters Patent ofthe United Statesis:

1. A photographic silver halide emulsion containing a compound selectedfrom those represented by the following general formula:

wherein R represents a member selected from the group consisting of ahydrogen atom, an alkyl group, a benzothiazyl group, a benzoxazyl group,and a pyridyl group and D represents the non-metallic atoms necessary tocomplete a benzene ring.

2. A photographic silver halide emulsion as defined in claim 1 whereinthe silver halide emulsion is a gelatinosilver halide developing-outemulsion.

3. A photographic gelatino-silver-halide developing-out emulsion asdefined in claim 2 wherein the silver halide is silver bromiodide.

4. A photo-graphic gelatino-silver-halide developing-out emulsioncontaining a compound selected from those represented by the followinggeneral formula:

C/ ll wherein R represents a member selected from the group consistingof a hydrogen atom, an alkyl group, a hen zothiazyl group, a benzoxazylgroup, and a pyridyl group.

5. A photographic gelatino-silver-halide developing-out emulsioncontaining a compound selected from those represented by the followinggeneral formula:

(in. C/

wherein R represents an alkyl group containing from l to 4 carbon atoms.

6. A photographic gelatino-silver-halide developing-out emulsioncontaining a compound selected from those represented by the followinggeneral formula:

(fun 15 wherein R represents a benzothiazyl group.

7. A photographic silver-halide emulsion containing the compoundrepresented by the following formula:

V @s \N H 8. A photographic silver-halide emulsion containing thecompound represented by the following formula:

9. A photographic silver-halide emulsion containing the compoundrepresented by the following formula:

10. A photographic silver-halide emulsion containing the compoundrepresented by the following formula:

wherein R represents a member selected from the group consisting of ahydrogen atom, an alkyl group, a henzothiazyl group, a benzoxazyl group,and a pyridyl group, and D represents the non-metallic atoms necessaryto complete a benzene ring.

References Cited in the file of this patent UNITED STATES PATENTS1,725,934 Reitstotter Aug. 27, 1929

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A COMPOUND SELECTEDFROM THOSE REPRESENTED BY THE FOLLOWING GENERAL FORMULA: